The present study is part of a long-term investigation testing the hypothesis that the striatal complex is basically involved in organizing the expression of species-typical, prosematic (nonverbal) communication. The striatal complex is an evolutionary ancient part of the forebrain comprised of the olfactostriatum, corpus striatum (caudate and putamen), globus pallidus, and satellite collections of gray matter. In previous experiments it was found that lesions of the medial segment of the globus pallidus or interruption of its projections resulted in an elimination or fragmentation of the mirror display of "gothic-type" squirrel monkeys. Recovery of the display might occur after interruption of the pallidothalamic projections, but not the pallidotegmental projections. The present experiments represent a continuing effort to learn whether or not the thalamic or the midbrain tegmentum is more essential for the full expression of the display.